I am wondering because CCTV cameras usually have there resolution in TV lines (480tvl,700tvl etc.
Its a hangover from the analogue days and it's almost always also completely fanciful. It was an indicator of the frequency response of the system but it was most often measured *at* the imager and what you got out of the BNC on the back was rarely within a bulls roar of what the spec sheet said you'd get, particularly when things went colour. After you shoved it down some cheap, badly matched coax that had been stretched by the grunt installing it and then put it into a third world sourced monitor or VCR any resemblance to the spec sheet resolution was at most purely coincidental.
On well made systems with excellent quality cabling and due care and attention paid to the installation and termination (read "an expensive install) you could often get over half the resolution the piece of paper said you would.
Having said that, IP cameras are no better. I tested some 16 megapixel units recently that produced less than half the rated real resolution at the recorder because the spec sheet lists the imager resolution and pays no attention to the mush the badly implemented compression algorithms make of what was likely a pretty nice image. It's a common problem across the industry and often leads to horiffic issues if the footage has to go to court because an expert (and these guys are as close as you'll get to one) points out that at the supplied resolution there is reasonable doubt as to the identity of the block of pixels accused of the crime.
Never, _ever_ believe a salesman, spec sheet or manufacturer data. If you can't test it yourself, get a professional to do it for you and if you think you can test it adequately yourself, you are probably wrong.
Welcome to the security industry, the last holdout of the theif and charlatan.